The application relates generally to data storage enclosures, and relates more particularly to improved data storage enclosures made of cast magnesium or other non-ferrous material and held together with rivets.
There are many constraints on the mechanical design and manufacture of an enclosure for a data storage system. The enclosure must be strong. It needs to have myriad features to accomplish many design requirements, including guideways for receiving disk drive carriers and other devices. It should not cost too much to manufacture and should not be too heavy. Yet it must be constructed to rather close dimensional tolerances so that each piece aligns properly with its neighbors.
Most computer data storage systems are traditionally rack-mounted in industry-standard nineteen-inch racks. Each system is thus of a width to fit in the rack, and is of a height to accommodate the height of a disk drive. A plurality of disk drives are mounted in the system, parallel to each other and stacked to reach nearly the width of the rack.
Historically, computer data storage enclosures have been made of formed and fastened steel sheet metal. Such enclosures are composed of numerous discrete parts that require accurate manufacturing and assembly techniques in order to insure proper fit, form, and function. If this level of precision is not met an assortment of problems can result. These maladies can range from an enclosure""s inability to contain Electro-magnetic emissions to the generation of hard and soft errors from rotational vibration between adjacent disk drives. In addition to maintaining control over the structural aspects of the enclosure, it is also important to keep the drives and power supplies from overheating, so system cooling is paramount. Such cooling can be accomplished by a combination of forced-air cooling and inter-material conduction. The bulk material of a steel sheet metal enclosure often contributes little to cooling, and in fact may impede cooling. It is additionally necessary to provide plenums or other air guides so that cooling air from the system""s internal blowers can pass over each of the disk drives. It would be unacceptable for any disk drive to be starved of cooling air.
It is necessary to provide guideways which permit sliding disk drives into the enclosure. The guideways must satisfy many requirements, for example, they must cause the disk drive""s connectors to align with corresponding connectors on a backplane inside the enclosure. The guideways must also be spaced and shaped to within particular tolerances simply to receive the disk drives. The guideways must provide locking mechanisms to lock disk drives into place, yet must permit a drive to be readily unlocked for removal.
Typically, a sheet metal enclosure is relatively expensive to fabricate, especially considering the very demanding requirements for guideways and air plenums. Even with the use of thin gage sheet metals these enclosures are traditionally heavy which make them hard to handle and ultimately expensive to ship. There is thus a great need for an enclosure for a disk storage system that keeps its shape well, that provides guideways for disk drives, that allows for easy provision of air plenums, that helps rather than hinders cooling, that doesn""t weigh as much, and that can be economically manufactured.
One approach to this need is to use an enclosure made of cast magnesium or other non-ferrous parts. Two cast magnesium parts can be designed which, when combined, form an enclosure which substantially fulfills the needs just discussed. The further difficulty, then, is to devise a way of fastening the two parts. If sheet metal parts were used, it would be possible to employ any of a variety of fastening techniques, including spot welds, self-tapping sheet metal screws, machine screws and captive nuts, or rivets. But where cast magnesium parts are used, there are concerns about brittleness of the cast parts. Many cast metals do not weld well. Many combinations of screws and nuts present galvanic problems due to juxtaposition of dissimilar metals. More importantly, any fastening technique that requires driling of holes presents the further problem that it is necessary to worry about whether the holes have been drilled in the right place. This makes screws and nuts disfavored, and likewise disfavors nearly all riveting techniques that call for predrilled holes.
One commercially successful riveting system is that disclosed in U.S. Pat. No. 4,130,922 to Koett. This patent describes a headless riveting system in which a headless rivet is made from steel or a suitable material that provides compressive strength superior to that of the materials to be riveted together and of a height or thickness equal to the sum of the materials to be riveted. In this system, the rivet has flat or concave end surfaces and its body is peripherally concave between its ends. A die and punch are used to drive the rivet through the materials to be fastened. The rivet pierces the materials, comes to rest embedded in the materials, and the materials flow radially against the concave body of the rivet. The patent teaches, however, only that the materials are sheet materials, for example sheet steel or sheet aluminum. There is no mention in the patent that materials other than sheet materials can be joined with such rivets. Indeed, as a general matter the possible brittleness of a cast magnesium material would prompt one skilled in the art to rule out the use of self-piercing rivets as distinguished from rivets that are inserted into pre-drilled holes.
There is thus a great need for a fastening technique that works well with cast magnesium parts to permit fabrication of a high-quality enclosure for a data storage system. Stated differently, there is a great need for a high-quality enclosure for a data storage system, composed of cast magnesium parts that are reliably fastened together in compliance with exacting tolerances.
An enclosure for a data storage system comprises at least first and second cast non-ferrous parts such as magnesium parts joined by rivets, each of which is made of a suitable material that provides compressive strength superior to that of the cast metal. Each rivet is of a height or thickness equal to the sum of the thickness of the parts to be riveted. Each such rivet has flat end surfaces and its body is peripherally concave between its ends. The rivet is embedded in the two parts, and the parts flow radially against the concave body of the rivet. No drilling is required, and the parts are held in carefully defined position while being joined, so that the assembled enclosure satisfies strict dimensional tolerances.